Unforgiveness as a sin is sometimes worse than murder. I do not say that it is worse than all murders.
Murder can be a done in the heat of passion but not forgiving someone is done in the heart of the person. One has to make a decision in the heart to not forgive someone. It is a conscious decision in one’s heart.
The truth is, is one can also make a decision in one’s heart to forgive as well. God wants to deal with our heart, to clean out that sin of unforgiveness that would kill us. Unforgiveness does not harm the one we do not want to forgive but harms us. It is like a cancer slowly taking over our hearts and minds and replaces everything that is good in us.
If one looks at the greatness of the debt that God has forgiven you and me; that we rejected Him, that we fought against Him in our hearts, that we denied Him and his love for us may times; one cannot help but ask God to give one the ability to forgive the one who has hurt or harmed you. The Holy Spirit will strengthen you when you make that decision to forgive. The Holy Spirit wants to show you Christ Jesus, Him Crucified for your sin; risen from the dead and glorified as God’s life-giving Spirit so that you may live in Him. This revelation of you in Christ, His life, living though you will enable you to forgive.
With forgiveness comes the freedom to also love that person.